Conclusions - Summary and Conclusions - 鋼骨托梁抗彎接頭含梯度漸擴式梁翼板之耐震行為

Chapter 8. Summary and Conclusions

8.2 Conclusions

The main objectives of this research are to identify and clarify the design variables of a tapered flange, to investigate the behavior of the connection under cyclic loading, and to provide design recommendations for tapered flange moment connections. The following summarizes the major observations and findings in this dissertation:

Performance of pre-Kobe connection

1. Localized principle stresses and plastic equivalent strains, concentrated at either the tips of the beam flange groove welds or the root of the WAH, were noticed in a finite element model of the pre-Kobe connection. This observation can be attributed to the cross section of the column and the geometry of the WAH configuration, respectively. The potential for crack initiation at these locations are very high, probably causing the beam flange to fracture.

2. The WAHs significantly affect the ductility of a connection. Test of the pre-Kobe connection specimen demonstrated appropriate ductile behavior of 2.6% rad plastic rotation but failed in brittle flange fracture at a story drift angle of 4% rad.

Cracks were observed in the fusion zone of the sides of the beam flange groove weld during the 3% rad cycles; the other crack initiated in the toe of the WAH during the 4% rad cycles. The primary account dominating the failure of this specimen is the presence of the WAHs in the beam web. Using column-tree

design practice in the connection has little effect on the prevention of the flange fracture originated from the WAH region.

Effects of tapered flange geometry

1. The behavior of a tapered flange connection is mainly influenced by the length of a tapered zone in the beam and a flange reinforcement ratio at the beam-to-column interface, along with the length of a main tapered flange enlargement and tapered flange extension.

2. Results of the analytical parametric study revealed the following: (1) higher flange reinforcement increases the capacity of the CJP groove welds and results in higher margin of safety at the beam-to-column joint; (2) the larger tapered zone of the beam flange causes lower plastic strain demand at the CJP welds and the WAH region; and (3) using the larger tapered flange enlargement can move away the plastic deformation from the column face.

Performance of tapered flange connections

1. Analytical examinations of the tapered flange connection exhibited extensive plastification spread around the tapered region of the beam away from the column face.

2. Experimental investigations demonstrated that only one of total six tapered flange connections (specimen W3-L03) took place unexpected crack initiation and propagation starting at the fusion zone of the CJP groove weld. No weld fracture was observed in all of other test specimens. This indicates that using the adequate width of the tapered flange at the beam-to-column joint can remarkably prevent

premature flange fracture in welds.

3. Test results also show that local buckling occasion of the specimens could be delayed because the tapered beam flange provided an extensive uniform yielding in the beam. These specimens sustained a sufficient rotation of 5% rad story drift angle, satisfying the requirements for connections used in SMFs. The ductility of the moment connection is successfully improved by the application of the tapered flange.

4. The extra cost for fabricating such built-up tapered flange connection is relatively high, compared to the traditional unreinforced connection. However, this new style of moment connections, using either the column-tree or the pre-Northridge design practice in the connection, can perform good ductile behavior and result in the stable energy dissipation.

Implication of frame analysis

1. The nonlinear static pushover analyses performed in both frames demonstrate that the globally structural behaviors of steel SMFs, such as strength degradation and yield sequences, are reasonably evaluated by using the verified connection models. The pushover analysis, as a result, can be used as an efficient design procedure for the performance evaluation of buildings under some concerned performance levels.

2. SMFs with unreinforced connections exhibited limited inelastic behavior with the amount of connections failed, which caused 17% and 75% strength reduction in five- and fifteen-story frames, respectively, at the CP performance level. On the contrary, large inelastic deformation with a steady post-yielding behavior is

observed in the TF frames. Significantly, the ductile capability of the TF frames is larger than that of the UR frames.

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Table 3.1 Parameters used in finite element analysis

Parameter Geometry

Model No. β^j

L w

(b ) _f

L tap

(d ) _b

L ext

(d )_b

Max. width of beam flange

(mm)

Length of stub beam

(mm) Note

1 1.00 －－－ 300 1000 Pre-Kobe type

2 1.05 0.50 0.30 0.50 372 760

3 0.50 394 900

4 0.80 430 1110

5 1.10 0.50 0.30 0.50 395 760

6 0.50 416 900

7 0.80 455 1110

8 1.20 0.50 0.30 0.50 440 760 Control model

9 0.25 440 585

10 － 440 410

11 0.50 0.50 463 900

12 0.80 505 1110

13 0.33 0.30 430 710

14 0.17 422 660

15 1.25 0.50 0.30 0.50 460 760

16 0.50 486 900

17 0.80 530 1110

Table 4.1 Material properties of test specimens Member Coupon

Yield strength,F_y (MPa)

Tensile strength,F_u (MPa)

Beam flange 387 507

Link beam

Beam web 429 529

Beam flange 371 511

Stub beam

Beam web 373 494

Column Column flange and web 431 578

Table 4.2 Details of test specimens Specimen* β^j

Ltap

(d ) _b Beam web joint detail

PK －－ Fillet welded web

W1-L05 1.20 0.5 Fillet welded web W1-L03 1.20 0.3 Fillet welded web W2-L03 1.10 0.3 Fillet welded web W3-L03 1.05 0.3 Fillet welded web B1-L03 1.20 0.3 Bolted shear tab B2-L03 1.10 0.3 Bolted shear tab

*All specimens consist of an H-shaped H700×300×13×24 beam (dimensions in mm for depth, width, web thickness, and flange thickness, respectively) and a built-up box 550×550×28×28 column.

Table 4.3 Overview of test results Specimen

Total story drift rotation (% rad)

Total plastic rotation (% rad)

Beam plastic

rotation (% rad) Failure mode

＋4.0 ＋2.6 ＋2.4

*Test was stopped due to the stroke limitation of the actuator.

Table 5.1 Percentage of beam shear force for specimen W1-L03 Distance from column face (mm)

Drift level Shear component 20 200 410 760

Beam web (%) 52 91 95 95

Table 7.1 Dead loads for studied buildings

Equivalent uniform load Description (N/m ) (² kgf/m ) ² Slab (15 cm deep, lightweight concrete) 1,766 180 Metal deck (thickness of 1.2 cm, ALK 12) 147 15

Ceiling 245 25

Mechanical/Electrical 491 50

Fireproofing 98 10

Raised floor 589 60

Asphalt paving (only impose at roof) 785 80

Curtain wall 785 80

Total Roof 3,532 360 Floors 4,120 420

Table 7.2 Live loads for studied buildings

Equivalent uniform load Description (N/m ) (² kgf/m ) ²

Office occupancy 2,943 300

Partitions 981 100

Total Roof 2,943 300 Floors 3,924 400

Table 7.3 Distribution of design seismic forces for studied frames Model

name Floor

level Lateral earthquake forces

(kN) Story shear forces (kN)

Table 7.4 Tapered flanges used in studied frames Tapered flange size Model name Beam size

Table 7.5 Confidence levels for different confidence parameters λ with hazard parameterk=4.62 Confidence level

Uncertainty

βUT 2% 5% 10% 20% 30% 40% 50% 60% 70% 80% 90% 95% 99%

0.1 1.26 1.21 1.16 1.11 1.08 1.05 1.02 1.00 0.97 0.94 0.90 0.87 0.81

0.2 1.65 1.52 1.42 1.30 1.22 1.15 1.10 1.04 0.99 0.93 0.85 0.79 0.69

0.3 2.28 2.02 1.81 1.58 1.44 1.33 1.23 1.14 1.05 0.96 0.84 0.75 0.61

0.4 3.29 2.79 2.42 2.03 1.78 1.60 1.45 1.31 1.17 1.03 0.87 0.75 0.57

0.5 4.97 4.06 3.38 2.71 2.32 2.02 1.78 1.57 1.37 1.17 0.94 0.78 0.56

0.6 7.87 6.16 4.96 3.81 3.15 2.67 2.30 1.97 1.68 1.39 1.06 0.86 0.57

Example:

For the case of TF-15F at the global CP performance level, given Uncertainty coefficient β_UT=0.5

Confidence parameters λ =0.96

Using linear interpolation between 0.94 (the corresponding confidence level=90%) and 1.17 (the corresponding confidence level=80%), the confidence level of 89% can be found.

Table 7.6 Confidence level evaluation for studied frames

Confidence level (%) Model name

Performance

level D ^C λ Analysis Code

IO (Global) 0.011 0.020 1.12 46 50

IO (Local) 0.011 0.020 1.24 49 50

CP (Global) 0.045 0.100 0.63 98 90

UR-5F

CP (Local) 0.045 0.030 1.98 13 50

IO (Global) 0.010 0.020 1.02 64 50

IO (Local) 0.010 0.020 1.13 61 50

CP (Global) 0.045 0.100 0.63 98 90

TF-5F

CP (Local) 0.045 0.050 1.19 62 50

IO (Global) 0.013 0.020 1.24 28 50

IO (Local) 0.013 0.020 1.38 36 50

CP (Global) 0.064 0.085 1.43 67 90

UR-15F

CP (Local) 0.064 0.030 3.38 1 50

IO (Global) 0.011 0.020 1.05 58 50

IO (Local) 0.011 0.020 1.16 58 50

CP (Global) 0.043 0.085 0.96 89 90

TF-15F

CP (Local) 0.043 0.050 0.97 56 50

Beam Column

Shear tab Continuity plate

CJP groove weld

Beam bottom flange Column

flange

Backing

Weld access hole Field welded by CJP weld Beam top flange

Field welded by CJP weld

Weld access hole Column flange Backing

Figure 1.1 Connection details of web-bolted flange-welded pre-Northridge moment connection.

Beam Box column Shear tab

SESNET

electroslag welding CJP groove

welding

B B

A A

Diaphragm

Section A-A Section B-B

Figure 2. 1 Connection details between H-shaped beam and welded built-up box column.

SESNET

Diaphragm Box column

Weld metal

Backing bar

Figure 2.2 A schema of SESNET electroslag welding.

Cover plate Wing plate Column Beam Column Beam

Shear tab Continuity plate

Haunch Column

Beam

Rib plate Column

Beam

Figure 2.3 Examples of reinforced moment connections.

Figure 2.4 Reinforced moment connection with wing plates. (陳嘉有 1995)

Constant cut

Radius cut

Tapered cut Figure 2.5 Different RBS configurations

(a) (b)

Beam flange

r

Column flange

CJP weld

r

Figure 2.6 Weld access hole configurations: (a) a quarter-circular shape; (b) a modified shape recommended by FEMA-350.

Shop welded

joint Field splice Column-tree

Link beam

Stub beam

Figure 2.7 Steel column-tree moment frame

(a)

Stub beam

Field bolted by high-strength bolts Square tube or column

CJP weld fillet weld

CJP weld

Through

diaphragm Beam bottom flange Weld access hole

Shop welded by CJP groove weld

(b)

Stub beam

Field bolted by high-strength bolts Box column

CJP weld fillet weld

CJP weld

Interior diaphragm

Weld access hole

Beam bottom flange

Shop welded by CJP groove weld

Figure 2.8 Typical pre-Kobe column-tree connections: (a) Through-diaphragm connection; (b) Interior-diaphragm connection.

Box column

Stub beam Widened flange

Figure 2.9 Widened flange connection configuration. (Chen et al. 2006)

-6 -4 -2 0 2 4 6

Total plastic rotation (% rad) -1

0 1

Normalized moment (M/Mp)

W10-L2

-6 -4 -2 0 2 4 6

Total plastic rotation (% rad) -1

0 1

Normalized moment (M/Mp)

W08-L1

Figure 2.10 Normalized moment versus total plastic rotation curves for specimens W10-L2 and W08-L1. (Chen et al. 2006)

Box column

Link beam

Lext

Ltap

Lw1 Lw2

R Uniform yielding scope Tapered zone

Figure 2.11 Geometry of tapered flange connection

(a) (b)

Flexure capacity Mp,j

Mdem,j

Link beam

Moment demand Box column

C L

Moment

Stub beam with tapered flange

Flexure capacity Link beam Box column

Moment demand

C L

Moment

Stub beam with widened flange

Figure 2.12 Comparison with seismic moment demand and flexure capacity: (a) for tapered flange connections; (b) for widened flange connections.

Figure 3.1 Geometry of 3-D structural solid element SOLID45 (ANSYS 2002)

Monotonic loading

Link beam H700×300×13×24 Box column

550×550×28×28 Roller

Pinned support

Symmetric plane

Stub beam

Figure 3.2 Boundary conditions and meshes of finite element model.

(a)

R2=10 mm

R1=30 mm 10 mm 5 mm

35°

Beam top flange

Beam web

(b)

R2=10 mm R1=30 mm 10 mm

5 mm

35°

Beam bottom flange Beam web

Figure 3.3 Details of weld access hole.

(a)

CJP weld

Weld access hole

Column-tree Box column CJP groove weld

Fracture plane

(b)

CJP weld

Weld access hole

Column-tree Box column Root of WAH

Fracture plane

Figure 3.4 Critical sections of pre-Kobe connection: (a) at CJP groove weld; (b) at root of WAH.

(a)

-200 -100 0 100 200

Distance from beam flange centerline (mm) 0.0

0.5 1.0 1.5

Normalized principal stress (σ1/Fy)

Pre-Kobe

Distance from beam flange centerline (mm) 0.0

0.5 1.0 1.5

Normalized principal stress (σ1/Fy)

Pre-Kobe

Distance from beam flange centerline (mm) 0

Figure 3.5 Distributions of normalized principal stresses and PEEQ indices along beam flange width at CJP weld and root of WAH: (a) normalized principal stress at 0.5% rad story drift angle; (b) PEEQ indices at 4% rad story drift angle.

(a)

1.0 1.1 1.2 1.3

Parameter β_j 0

10 20 30 40

PEEQ index

L_tap= 0.3d_b L_tap= 0.5d_b L_tap= 0.8d_b Pre-Kobe type

28.02

Sides of CJP weld

(b)

1.0 1.1 1.2 1.3

Parameter β_j 0

10 20 30 40

PEEQ index

L_tap= 0.3d_b L_tap= 0.5db

L_tap= 0.8d_b

Pre-Kobe type

21.65

Root of WAH

Figure 3.6 Effect of different values of parameter β_j and length of tapered part L on PEEQ indices at 4% rad story drift angle: (a) at borders of CJP tap

weld; (b) at root of WAH.

28.0 Side of CJP weld

Figure 3.7 Effect of length of main tapered flange reinforced part L on PEEQ _w₁ indices at 4% rad story drift angle.

-150 -75 0 75 150

Distance from beam flange centerline (mm) 0

Figure 3.8 Effect of length of tapered flange extension L on PEEQ indices along _ext root of WAH between column-tree and link beam at 4% rad story drift angle.

Symmetrical plane

(a) Pre-Kobe connection (b) Tapered flange connection (L_tap =0.3d_b)

Box column

Figure 3.9 Longitudinal plastic strain contours for different configuration of connections during 4% rad story drift angle.

Symmetrical plane

(a) Pre-Kobe connection (b) Tapered flange connection (L_tap =0.3d_b)

Figure 3.10 Contour plots of plastic equivalent strain for different configurations of connections at 4% rad story drift angle.

TYP.

1000 Box column

□550×550×28×28

Link beam H700×300×13×24

Unit: mm

R30R10 10 5 35°

10 5 35°

5 5

TYP.

Figure 4.1 Connection details of specimen PK.

350

10 W1-L03 W2-L03

R100

Unit: mm

R150

150 350 50

345

465

Box column

□550×550×28×28

Link beam H700×300×13×24 R150

150 350 210

50 326 440 for W1-L03 395 for W2-L03

100 210 350

325

W1-L05

W3-L03

R30R10 10 5 35°

5 35°

5 5

TYP.

12 TYP.

365

Figure 4.2 Connection details of specimen W1-L05, W1-L03, W2-L03, and W3-L03.

10 TYP.

5 35°

TYP.

5@92 50 12

F10T M24

R30R10 20

PL560×195×20

150 350 210

50 326 440 for B1-L03 395 for B2-L03

Box column

□550×550×28×28

Link beam H700×300×13×24 R150

5 5

TYP.

Unit: mm

B1-L03 B2-L03

Figure 4.3 Connection details of specimen B1-L03 and B2-L03.

Link beam

Box column Tapered flange

Actuator

3600 mm

3000 mm Strong floor

Strong wall

Figure 4.4 Overall view of test setup

-5 -4 -3 -2 -1 0 1 2 3 4 5

Interstory drift angle (% rad)

Loading step

6 cycles 6 cycles 6 cycles

4 cycles 2 cycles

2 cycles 2 cycles 2 cycles

2 cycles

Figure 4.5 Loading history

Figure 4.6 The definition of story drift angle for test assembly (FEMA-350 2000)

Box column

Beam flange fracture

Figure 4.7 Failure mode of typical pre-Kobe specimen PK.

W3-L03

Beam flange fracture Tapered

flange plate Weld

access hole

Figure 4.8 Fracture of beam flange groove weld of specimen W3-L03 at 4% rad story drift angle.

(a)

W1-L05

Box column Tapered

flange

(b)

W1-L03

Box column Tapered

flange

Figure 4.9 Plastic hinge formation followed by local buckling at 5% rad story drift angle: (a) specimen W1-L05; (b) specimen W1-L03.

B1-L03

Crack

Figure 4.10 Slight cracking at root of weld access hole of specimen B1-L03 at 4%

rad story drift angle.

(a)

B1-L03

Box column Shear tab

(b)

B2-L03

Box column Shear tab

Figure 4.11 Local buckling of beam flanges and beam web at 5% rad story drift angle: (a) specimen B1-L03; (b) specimen B2-L03.

(a) (b)

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

Figure 4.12 Hysteresis response of specimen PK: (a) normalized moment at column face versus story drift angle; (b) normalized moment at column face versus total plastic rotation.

(a) (b)

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W1-L05

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W1-L05

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W1-L03

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W1-L03

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W2-L03

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W2-L03

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W3-L03

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

W3-L03

Figure 4.13 Normalized moment versus rotation responses of column-tree tapered flange connection specimens: (a) in terms of story drift angle; (b) in terms of total plastic rotation.

(a) (b)

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

B1-L03

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

B1-L03

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

B2-L03

-4 -2 0 2 4

Total plastic rotation (% rad) -1

0 1

Normalized moment at column face (M/Mp)

B2-L03

Figure 4.14 Normalized moment versus rotation responses of web-bolted flange-welded tapered flange connection specimens: (a) in terms of story drift angle; (b) in terms of total plastic rotation.

PK W1-L03 W2-L03

0 250 500 750 1000 1250

Distance from column face (mm)

0.0 0.5 1.0 1.5

Test moment /Capacity (Mtest/Mp)

1.15

Beam flange enlargement

Tapered zone Beam-to-column interface

Figure 4.15 Ratios of maximum test moment to calculated moment capacity of the specimens PK, W1-L03, and W2-L03 along the length of the beam.

(a)

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

Specimen W1-L05 W1-L03 W2-L03 W3-L03

(b)

-6 -4 -2 0 2 4 6

Story drift angle (% rad) -1

0 1

Normalized moment at column face (M/Mp)

Specimen B1-L03 B2-L03

Figure 4.16 Envelope relationships of normalized moment versus story drift angle:

(a) specimens with column-tree connection; (b) specimens with web-bolted flange-welded connection.

762

1796 1820 1797 1771 1780

1091

0 500 1000 1500 2000 2500

Energy dissipation (kN-m)

Specimen

B2-L03 W2-L

B1-L03 W1-L03

W1-L05 PK

W3-L03

Figure 4.17 Comparison of test specimen energy dissipation.

-200 -100 0 100 200

Beam tip displacement (mm) -1000

-500 0 500 1000

Beam tip load (kN)

-4 -2 0 2 4

Story drift angle (% rad)

TEST FEA

W1-L03

Figure 5.1 Comparison of experimental and analytical beam tip load versus beam tip displacement response of specimen W1-L03.

(a)

Figure 5.2 Position of strain gauges: (a) specimen PK; (b) tapered flange specimens.

Line F40

Target strain gauge

0 10 20 30 40

Normalized strain (

ε

_y) -225

-150 -75 0 75 150 225

Distance from beam flange centerline (mm)

TEST 0.5% drift 1% drift 2% drift 3% drift 4% drift FEA

0.5% drift 1% drift 2% drift 3% drift 4% drift

Line F40

Figure 5.3 Verification of longitudinal strain distributions at line F40 for specimen W1-L03.

104

Line TF1

Target strain gauge

Line TF2

Target strain gauge

Line TF3

Target strain gauge

0 10 20 30 40

Distance from beam flange centerline (mm)

在文檔中鋼骨托梁抗彎接頭含梯度漸擴式梁翼板之耐震行為 (頁 69-151)